Process for the preparation of methylolacrylamide



UnitedStates Patent s me QQ Patented Nov. 13, 1962 adhesives, fibers, surface coatings, paper, textiles and the 3,064,050 like, the need for an economically feasible process PROCESS FOR THE PREPARATION OF without any of the attendant disadvantages and hazards METHYLQLACRYLAMIDE found in prior art methods is very desirable.

Kenneth W. Saunders Darien Conn. and Louis L. t tv t 's Lento, J12, orth Scituate, M ass assignors to Amer- 5 A principal Objec of the presen m en Ion 1 an 1m can Cyanamid Company, New York N'Yqa corPorw proved process for the preparation of methylolacrylfi f Maine amide whereby the disadvantages of prior art methods N D i Filed J 3 9 1 89 012 are avoided. A further object of the present invention is 4 Claim (Cl, 260 561) to prepare solid, well defined crystalline monomeric 10 methylolacrylamide useful in the preparation of poly- This invention relates to the preparation of N-alkylol mers. Another object of the present invention is to unsaturated amide monomers. More particularly it re provide a method for the preparation of methylolacryllates to an improved process for preparing methyiolamide from readily accessible starting materials wherein acrylamide. multiple costly processing steps are avoided. A still Heretofore numerous proposals have been adv nced further object of the present invention is to prepare subfor the preparation of N-alkylol unsaturated amides from stantially pure methylolacrylamide from acrylamide and the corresponding unsaturated amide and an aldehyde. an aldehyde in high yields. A still further object of In each of the proposed methods marked disadvantages the present invention is to provide a process for ave been found More often than not, such disadvanpreparing methylolacrylamide usin carefully controlled tages have seriously hampered widespread commercial conditions for their preparation in an all water sysexploitation of these processes for preparing N-alkylol term. It has now been discovered that acrylamide may unsaturated amides. us, in one metho an aqueous be reacted with formaldehyde in an aqueous system solution of acrylamide has been reacted with an aqueous in which the amount of acrylamide constitutes at least methylolacrylamide in dilute aqueous solution. -The and water present in the system. Unexpectedly, the ultiprmcipal disadvantage of such procedure is that methylolmate yield of methylolacrylamide obtainable by such a acrylamide cannot be isolated directly us, evaporaprocess 18 extremely higher than that which might have two or azeotropic techn ques are required to concenbeen expected for an aqueous system 1n view of the in an easily recoverable form Which'is desired. 'Furtheri.e. methylolacrylamide, are both extremely soluble in methylolacrylamide are not satisfactory. it can be carried out at a temperature where polymdditionally, acrylamide has been reacted with paraeriza'tion is negligible even in the absence of an inhibitor. formaldehyde in both concentrated alcoholic solutions It is essential that the process be carried out in an t and in the presence of halogenated solvents. While aqueous medium wherein the amount of reactant, i.e. I either of these methods constitutes an improvement over acrylamide, is at least 60% and not more than 97% by the d' the aqueous method, nonetheless the use of toxic weight of the amount by weight of amide and Water orflammable solvents in the reaction constitutes'a very 40 present in system and preferably in an amount from distincthazard for semi-commercial or commercial procabout 75% to about 90% by Weight. If concentrations esses In addition to the potential hazards brought about lower than 60% are employed, dlfficu ty in recovering by the use of such solvents, special equipment and premethylolacrylamide Will be encountered and multiple cautions are required In clarification and filtration opera steps must be employed in order to achieve fair yields by trons urthermore, the use of such organic solvents ei e1 azeotropic recovery methods or evaporative techon a production scale requires a solvent recovery system niques Similarly if concentrations 0 acrylamide in order to bring about an economical process Moregreater than 97% are employed, spontaneous polymerizaover, additional processing is generally re uired in order tion of the startm material may result because of the to obtain a product which is substantially free of contamisubstantially higher temperature require nants and impurities. A further requirement of our novel process is the use Another method which has been employed for the prepof a basic catalyst to provide a pH of from about 8 to wherein solid acrylamide has been reacted with solid is 9 to 10. Among such catalysts paraformaldehyde. ee, for example, U.S.P. No. 2,864,- ployed there may be mentioned triet Even employing this process, however, numerous pylamine, tri-n-butylamine, potassium carbonate, sodium difiiculties are found. One hazard is the problem of carbonate, potassium hydroxide sodium hydroxide, barscale-up wherein it is exceedingly difiicult to dissipate ium hydroxide, sodium and potassium alkoxides e.g., sothe heat of reaction. In addition, the process is a dium ethoxide, multiple step one in that the solid methylolacrylamide droxide however, is'preferable.v In additio most frequently has to be recrystallized in order to achieve lytic amount of alkaline material bein a fairly uniform and pure product; In this process, tion system it violent polymerization of acrylamide upon fusion occurs. f acidic material It will thus be se 11 that while numerous expedients lent to the amount of acid present.

Neutralization of the have been tried, no one particular method offers a simacidic material enables the reaction to proceed more ple or easy route to the preparation of methylolacryb smoothly after the addition of catalyst. While formaldeamide. In view of the increased importance of methylolhyde per se may be used usually a source thereof such as acrylamide in recent years, an attractive commercial procparaformaldehyde, trioxane or the like is employed. Of ess for its preparation is highly desirable. Since the these, paraformaldehyde is preferred. Equimolecular polymerization and copolymerization proudcts of methamounts of the reactants i.e. acrylamide and formaldeylolacrylamide have wide applicability in such fields as hyde, are generally employed. owever, a slight excess preferable, however,

maintained at 50 of either reactant apparently does not affect the reaction.

The reaction may be conducted over a fairly wide temperature range. In general, temperatures ranging from about C. to about 90 C., have been employed. It is to employ temperatures from about to about 50 C., in order that the product may be recovered fairly easily without expensive refrigeration. In view of the exothermic nature of the reaction, it may be desirable to cool the reaction mixture in order that possible polymerization of either reactants or the products may be forcstalled. The time of reaction will vary depending upon the amount of the reactants employed, catalyst, temperature and the like. In general, reaction times of from about one-half hour to about twenty-four hours are satisfactory.

A polymerization inhibitor such as sodium nitrite or cupferron may be incorporated in the system to prevent polymerization. Generally, however, the use of such an inhibitor is not required when the reaction temperatures are below about C.

The methylolacrylamide product is easily separated from the product solution by crystallization. Cooling of the solution to about 20 C. or lower to effect such separation of crystalline product is preferred. The product is filtered from the reaction mixture and air-dried. By subsequent recycling of mother liquors recovered from separation of product methylolacrylamide, the ultimate yield of product can be increased to almost 100% from once through yield of from about 60 to 80%.

In order to illustrate the method of conducting the present invention the following examples are given.

Example 1 To a suitable reaction vessel containing 845 grams of water to which is added 0.85 gram of cupferron is charged 4370 grams of 96% acrylamide (59.4 moles) and the mixture is stirred at to C., until the acrylamide has dissolved. 120 cc. of triethylamine are added to raise the pH to 9.6. The temperature is maintained at 50 C., while charging 1890 grams of 96.6% paraformaldehyde (60.8 moles formaldehyde). The reaction is continued for a period of about two hours until the concentration of free-formaldehyde indicates that the reaction is substantially complete. The solution is cooled to 15 C., and solid crystals of methylolacrylarnide (29.3 moles) are removed from the solution with suction. The solid methylolacrylamide collected together with the methylolacrylamide in the filtrate (recycle liquor) represented an almost quantitative yield.

Example 2 The procedure of the Example 1 is repeated in all material respects except that the acrylamide is neutralized prior to reaction to its equivalence point, pH 9.8, with 50% sodium hydroxide solution followed by the addition of 50 cc. of triethylamine. After about one hour reaction time followed by the cooling of the solution to about 15 C., 28.0 moles of methylolacrylamide, M.P. 758 C., are recovered. The once through yield of methylolacrylamide is thus 47% and the ultimate yield is nearly quantitative. The melting point of methylolacrylamide recrystallized five times from alcohol is 76.5- 77.7 C., thus indicating that a product of a high degrree of purity is obtained.

Example 3 The procedure of Example 1 is repeated except that following the addition of 96% acrylamide the solution is adjusted to pH of 8.0 with 50% NaOH solution and triethylarnine. Subsequently, paraforrnaldehyde is added with stirring while the temperature of the reaction is C. as in Example ,1. Reaction is conducted for a period of about one-half hour and. solid crystalline acrylamide, MI. 77-'79 C., is recovered upon cooling of the reaction mixture to 8 C. The once is one-half hour.

Example 4 is charged 423 grams of acrylamide to which is To a suitable reaction vessel water and 2200 grams of 96% added 0.43 gram of cupferron. The acrylamide slurry is heated to about 50 C. at which time 21 cc. of 50% NaOH solution is added both as a neutralizing agent and as a catalyst. The pH of acrylamide solution after addition of NaOH was 9.8. The temperature is maintained at 50 C. and then paraformaldehyde (96.6%) amounting to 940 grams is added with stirring. Reaction time Subsequently, the reaction mixture is C. and is filtered. The once through the ultimate yield exceeds cooled to 10-15 yield is 45% and Example 5 To a suitable reaction vessel is charged 13 lbs. of water and 67 lbs. of 96% acrylamide. The pH of the slurry is then adjusted to 9.8 with 50% NaOH solution. While maintaining the temperature of the acrylarnide slurry at 3040 C., 29.3 lbs. of 96.6% paraforrnaldehyde are added with stirring. The reaction is allowed to continue at 3040 C., for a he reaction mixture is then cooled to 16 C. and filtered to recover 45.2 lbs. of methylolacrylarnide, MP. 7577.5 C., a once through Recycling of the mother liquor affords an I amount of product which when added to the amount previously recovered of two hours.

Example 6 To a suitable reaction vessel is charged 189 lbs. of water which is heated to 50 C. Cupferron, 0.1 lb. is then added. Subsequently, 995 lbs. of acrylamide are added with stirring w ile maintaining the temperature at 45 to 50 C. The pH is adjusted to about 9.5 with 50% NaOH solution. The solution is then cooled to 30 C. with stirring over a two hour period. While maintaining the temperature at 25 to 30 C. and pH at 9.5, 420 lbs. of paraformaldehyde are added, The reaction mixture is stirred at 30. C. until the reaction is substantially complete as indicated by the free formalde hyde content being less than 2%. The solution containing the product is clarified and cooled to about 23 C. Methylolacrylamide crystals are added to the clarified liquor to induce precipitation. The crystalline material which readily precipitates is separated by centrifuge and is subsequently dried. Subsequent recycling of mother liquor affords an ultimate yield of 1340 lbs. of methylolacrylamide amounting to 98% based upon acrylamide.

We claim:

1. A process for preparing methylolacrylamide which comprises bringing V in an aqueous medium at a pH of from about 8 to about 11 equimolecular quantities of acrylamide and formaldehyde at a temperature between about 20 C., and. about 90 C., said acrylamide being present in an amount from about 60 to about 97% by weight of said acrylamide. and Water of said aqueous medium, and recovering methylolacrylarnide.

2. A process as in claim 1 in which said acrylamide is present in an amount from about 75% to about 90% by weight of said acrylarnide and water of said aqueous medium.

3. A process as in claim 1 in which the reaction is conducted at a pH of from about 9 to about 10.

4, A process as in claim 2 in which formaldehyde is present as paraforrnaldehyde.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PREPARING METHYLOCACRYLAMIDE WHICH COMPRISES BRINGING INTO REACTIVE CONTACT IN AN AQUEOUS MEDIUM AT A PH OF FROM ABOUT 8 TO ANOUT 11 EQUIMOLECULAR QUANTITES OF ACRYLAMIDE AND FORMALDEHYDE AT A TEMPERATURE BETWEN ABOUT 20*C., AND ABOUT 90*C., SAID ACRYLAMIDE BEING PRESENT IN AN AMOUNT FROM ABOUT 60 TO ABOUT 97% BY WEIGHT OF SAID ACRYLAMIDE AND WATER OF SAID AQUEOUS MEDIUM, AND RECOVERING METHYLOLACRYLAMIDE. 